LibJS: Use a premade shape for NativeFunction with length and name

~2% of the Speedometer 2.1 profile was just repeatedly performing the
shape transitions to add these two properties. We can avoid all that
work by caching a premade shape.

Libraries/LibJS/Runtime/FunctionObject.cpp

@@ -24,14 +24,10 @@ FunctionObject::FunctionObject(Object& prototype, MayInterfereWithIndexedPropert
 }
 
 // 10.2.9 SetFunctionName ( F, name [ , prefix ] ), https://tc39.es/ecma262/#sec-setfunctionname
-void FunctionObject::set_function_name(Variant<PropertyKey, PrivateName> const& name_arg, Optional<StringView> const& prefix)
+GC::Ref<PrimitiveString> FunctionObject::make_function_name(Variant<PropertyKey, PrivateName> const& name_arg, Optional<StringView> const& prefix)
 {
     auto& vm = this->vm();
 
-    // 1. Assert: F is an extensible object that does not have a "name" own property.
-    VERIFY(m_is_extensible);
-    VERIFY(!storage_has(vm.names.name));
-
     String name;
 
     // 2. If Type(name) is Symbol, then
@@ -74,8 +70,22 @@ void FunctionObject::set_function_name(Variant<PropertyKey, PrivateName> const&
         }
     }
 
+    return PrimitiveString::create(vm, move(name));
+}
+
+// 10.2.9 SetFunctionName ( F, name [ , prefix ] ), https://tc39.es/ecma262/#sec-setfunctionname
+void FunctionObject::set_function_name(Variant<PropertyKey, PrivateName> const& name_arg, Optional<StringView> const& prefix)
+{
+    auto& vm = this->vm();
+
+    // 1. Assert: F is an extensible object that does not have a "name" own property.
+    VERIFY(m_is_extensible);
+    VERIFY(!storage_has(vm.names.name));
+
+    auto name = make_function_name(name_arg, prefix);
+
     // 6. Perform ! DefinePropertyOrThrow(F, "name", PropertyDescriptor { [[Value]]: name, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }).
-    MUST(define_property_or_throw(vm.names.name, PropertyDescriptor { .value = PrimitiveString::create(vm, move(name)), .writable = false, .enumerable = false, .configurable = true }));
+    MUST(define_property_or_throw(vm.names.name, PropertyDescriptor { .value = name, .writable = false, .enumerable = false, .configurable = true }));
 
     // 7. Return unused.
 }

Libraries/LibJS/Runtime/FunctionObject.h

@@ -46,6 +46,8 @@ protected:
     explicit FunctionObject(Realm&, Object* prototype, MayInterfereWithIndexedPropertyAccess = MayInterfereWithIndexedPropertyAccess::No);
     explicit FunctionObject(Object& prototype, MayInterfereWithIndexedPropertyAccess = MayInterfereWithIndexedPropertyAccess::No);
 
+    [[nodiscard]] GC::Ref<PrimitiveString> make_function_name(Variant<PropertyKey, PrivateName> const&, Optional<StringView> const& prefix);
+
 private:
     virtual bool is_function() const override { return true; }
 };

Libraries/LibJS/Runtime/Intrinsics.cpp

@@ -212,6 +212,13 @@ void Intrinsics::initialize_intrinsics(Realm& realm)
     m_normal_function_name_offset = m_normal_function_shape->lookup(vm.names.name.to_string_or_symbol()).value().offset;
     m_normal_function_prototype_offset = m_normal_function_shape->lookup(vm.names.prototype.to_string_or_symbol()).value().offset;
 
+    m_native_function_shape = heap().allocate<Shape>(realm);
+    m_native_function_shape->set_prototype_without_transition(m_function_prototype);
+    m_native_function_shape->add_property_without_transition(vm.names.length, Attribute::Configurable);
+    m_native_function_shape->add_property_without_transition(vm.names.name, Attribute::Configurable);
+    m_native_function_length_offset = m_native_function_shape->lookup(vm.names.length.to_string_or_symbol()).value().offset;
+    m_native_function_name_offset = m_native_function_shape->lookup(vm.names.name.to_string_or_symbol()).value().offset;
+
     // Normally Realm::create() takes care of this, but these are allocated via Heap::allocate().
     m_function_prototype->initialize(realm);
     m_object_prototype->initialize(realm);
@@ -382,6 +389,7 @@ void Intrinsics::visit_edges(Visitor& visitor)
     visitor.visit(m_iterator_result_object_shape);
     visitor.visit(m_normal_function_prototype_shape);
     visitor.visit(m_normal_function_shape);
+    visitor.visit(m_native_function_shape);
     visitor.visit(m_proxy_constructor);
     visitor.visit(m_async_from_sync_iterator_prototype);
     visitor.visit(m_async_generator_prototype);

Libraries/LibJS/Runtime/Intrinsics.h

@@ -36,6 +36,10 @@ public:
     [[nodiscard]] u32 normal_function_name_offset() const { return m_normal_function_name_offset; }
     [[nodiscard]] u32 normal_function_prototype_offset() const { return m_normal_function_prototype_offset; }
 
+    [[nodiscard]] GC::Ref<Shape> native_function_shape() { return *m_native_function_shape; }
+    [[nodiscard]] u32 native_function_length_offset() const { return m_native_function_length_offset; }
+    [[nodiscard]] u32 native_function_name_offset() const { return m_native_function_name_offset; }
+
     // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct prototype
     GC::Ref<ProxyConstructor> proxy_constructor() { return *m_proxy_constructor; }
 
@@ -149,6 +153,10 @@ private:
     u32 m_normal_function_name_offset { 0 };
     u32 m_normal_function_prototype_offset { 0 };
 
+    GC::Ptr<Shape> m_native_function_shape;
+    u32 m_native_function_length_offset { 0 };
+    u32 m_native_function_name_offset { 0 };
+
     // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct prototype
     GC::Ptr<ProxyConstructor> m_proxy_constructor;
 

Libraries/LibJS/Runtime/NativeFunction.cpp

@@ -54,14 +54,16 @@ GC::Ref<NativeFunction> NativeFunction::create(Realm& allocating_realm, Function
     // 9. Set func.[[InitialName]] to null.
     auto function = allocating_realm.create<NativeFunction>(GC::create_function(vm.heap(), move(behaviour)), prototype, *realm.value());
 
+    function->unsafe_set_shape(realm.value()->intrinsics().native_function_shape());
+
     // 10. Perform SetFunctionLength(func, length).
-    function->set_function_length(length);
+    function->put_direct(realm.value()->intrinsics().native_function_length_offset(), Value { length });
 
     // 11. If prefix is not present, then
     //     a. Perform SetFunctionName(func, name).
     // 12. Else,
     //     a. Perform SetFunctionName(func, name, prefix).
-    function->set_function_name(name, prefix);
+    function->put_direct(realm.value()->intrinsics().native_function_name_offset(), function->make_function_name(name, prefix));
 
     // 13. Return func.
     return function;